Robert Shepherd and his sister Christianne died in October 2006
A brother and sister who died of carbon monoxide poisoning might have lived if their tour operator had carried out better checks, a Greek court has heard.
Thomas Cook employees, Nicola Gibson, 25, and Richard Carson, 27, are charged with the manslaughter by negligence of Robert and Christianne Shepherd.
The children, aged six and seven, died on a holiday in Corfu in October 2006.
District attorney Maria Tataki said: "Had the audits been more thorough the results may have been averted."
The children were on half-term holiday with their father Neil Shepherd, of Horbury, West Yorkshire, and his partner Ruth Beatson, who were both left in a coma as a result of the accident but survived.
Ms Tataki told Corfu Town courthouse on Monday that the Thomas Cook employees should have realised gas was being used in the bungalows.
She said: "I firmly believe that a tour operator like Thomas Cook should have conducted a more thorough check.
AT THE SCENE
Matt Cole, BBC News, Corfu
The day assigned for closing arguments quickly descended into a prolonged session of finger-pointing.
Lawyers took turns to stand and attempt to shift blame for Robert and Christianne's deaths, from their clients onto some or all of the other defendants.
Responsibility was moved around the courtroom as if on a merry-go-round, from employers to employees, from safety inspectors to engineering contractors.
Each lawyer began his statement promising to be brief. None was.
Sitting beneath a painting of Christ, the three judges began fidgeting and showing signs of restlessness.
Eventually the lead official snapped, explaining each counsel was there to defend their own client only and not to act as prosecutor for the others.
Watching on throughout, listening closely through translation headsets, were Robert and Christianne's parents, their long wait for justice perhaps finally nearing an end.
"It doesn't suffice to say that you trust the owners of the hotel, that you trust the managers of the hotel. No. It's not enough."
The court was told that Mr Carson had responsibility for filling out health and safety questionnaires, while Ms Gibson was an overseas representative.
Ms Tataki said they should have recognised that there were gas boilers present, even if the boilers were in outhouses next to the rooms and not in the rooms themselves.
But the court heard that Mr Carson accepted the hotel manager's information that there was no gas in the rooms.
The court heard how carbon monoxide fumes leaked into the bungalow from an outhouse next door where a "decrepit" boiler was leaking.
Public prosecutor Theodore Alissandratos told the court that Mr Carson should have at least asked what was in the outhouses.
He said: "He didn't perform a proper inspection of the area.
"The people who trust Thomas Cook with their vacation have the right to believe that they are safe.
"How can they be safe with an inspection like that? They can't be safe."
The court was told that if Thomas Cook had been alerted to the presence of gas boilers the company would have sent inspectors to check their safety.
A Thomas Cook spokesman said: "This accident happened because of a unique and unforeseeable set of circumstances for which neither Richard Carson or Nicola Gibson are responsible and should not be blamed in any way."
Nine Greeks, including the manager of the Louis Corcyra Beach Hotel in Gouvia, George Chrysikopoulos, are also on trial over the deaths.
The case continues.